Correlated metals as transparent conductors

Abstract

The fundamental challenge for designing transparent conductors used in photovoltaics, displays and solid-state lighting is the ideal combination of high optical transparency and high electrical conductivity. Satisfying these competing demands is commonly achieved by increasing carrier concentration in a wide-bandgap semiconductor with low effective carrier mass through heavy doping, as in the case of tin-doped indium oxide (ITO). Here, an alternative design strategy for identifying high-conductivity, high-transparency metals is proposed, which relies on strong electron–electron interactions resulting in an enhancement in the carrier effective mass. This approach is experimentally verified using the correlated metals SrVO3 and CaVO3, which, despite their high carrier concentration (>2.2 × 1022 cm−3), have low screened plasma energies (<1.33 eV), and demonstrate excellent performance when benchmarked against ITO. A method is outlined to rapidly identify other candidates among correlated metals, and strategies are proposed to further enhance their performance, thereby opening up new avenues to develop transparent conductors.

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Figure 1: Design rules for transparent conductors.
Figure 2: Structure and electrical transport properties of vanadate films.
Figure 3: Optical properties of vanadates.
Figure 4: First-principles calculation results of SrVO3.
Figure 5: Figure of merit ΦTC for transparent conducting materials.

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Acknowledgements

We gratefully acknowledge support by the Office of Naval Research through Grant No. N00014-11-1-0665 (L.Z., Y.Z., C.E., L.G., K.M.R., V.G., R.E.-H.), the National Science Foundation through the Penn State MRSEC Program DMR-1420620 (H.-T.Z., W.Z., M.H.W.C.) and Grant No. DMR-1352502 (L.Z., R.E.-H.), the Department of Energy through Grant DE-SC0012375 (M.B., R.E.-H.), the University of Toledo start up funds and the Ohio Department of Development (ODOD) Ohio Research Scholar Program entitled Northwest Ohio Innovators in Thin Film Photovoltaics, Grant No. TECH 09-025 (A.B., H.F.H., N.P.). We thank R. Averitt for stimulating discussions.

Author information

L.Z. and R.E.-H. conceived and designed the experiments. L.Z., H.-T.Z. and C.E. synthesized SrVO3 thin films. L.Z. and M.B. synthesized CaVO3 thin films. L.Z. performed XRD and AFM measurements. Y.Z. performed DFT calculations and Y.Z. and K.M.R. analysed the theoretical results. L.G. and V.G. performed optical transmission measurements. W.Z. and L.Z. performed the electrical transport measurements, and W.Z., L.Z. and M.H.W.C. analysed the results. A.B., H.F.H. and N.J.P. performed spectroscopic ellipsometry measurements and analysed the results for SrVO3 thin films. Y.X.Z. performed spectroscopic ellipsometry measurements and analysed the results for CaVO3 thin films. L.Z. and R.E.-H. wrote the manuscript and all authors gave comments on the manuscripts and approved the final version.

Correspondence to Roman Engel-Herbert.

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Zhang, L., Zhou, Y., Guo, L. et al. Correlated metals as transparent conductors. Nature Mater 15, 204–210 (2016). https://doi.org/10.1038/nmat4493

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